As shown in FIG. 1, the conventional method of establishing alignment between an end region of an optical fiber 4 and a laser diode 6 entails establishing rough alignment, e.g. by visual inspection through a microscope, and then energizing the laser diode so that it emits light into the proximal end region of the fiber and observing the optical power output at the distal end 8 of the fiber, for example by means of a photodiode 10 connected to a power meter 12. The position and orientation of the proximal end region of the optical fiber relative to the light emitting region of the diode are adjusted until peak power is obtained, and the optical fiber is then secured relative to the laser diode. The two elements may be secured together by bonding both elements to a common support member. This method of establishing alignment between an optical fiber and a laser diode is subject to the disadvantage that the performance of laser diodes is highly temperature dependent. Therefore, the output power at the distal end of the optical fiber depends not only upon the position and orientation of the proximal end region of the fiber relative to the light emitting region of the diode but also upon the temperature of the diode. Energization of the laser diode results in dissipation of heat, affecting the temperature of the diode and therefore accurate alignment of the fiber relative to the diode is difficult. Moreover, the conventional method of securing the optical fiber relative to the diode involves soldering, and the elevation in temperature associated with the soldering so affects the performance of the diode that it is not possible to confirm, at the time of soldering, that the fiber and the diode are properly aligned.